You should find entries with acpi and, more important, cpufreq_ondemand, which is responsible for on demand cpu frequency scaling. It reduces the speed at which you cpu runs and should therefore reduce the temperature.

You should also check the file
/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

It should contain the word "ondemand".

Prerequisite for all this is that you cpu supports frequency scaling, but since this is a Pentium M I guess that should be the case.

The fact that the GOVERNOR in /etc/sysconfig/cpuspeed doesn't seem to be a problem, because its also empty on my machine, which by the way runs cool. So if frequency scaling works on your machine, the hdd could be the problem. In order to veryfy that frequency scaling works, you could look into

/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq

It should show something below you max frequency (of course not if you are running something that puts a demand on you cpu).

With respect to your hdd, I am running ext4 too and haven't noticed that my hdd would overheat due to this. The temperature of the hdd is more dependent on how fast it spins. My laptop has a hdd that spins on a relatively low speed of 5400 rpm.

Additionally, which desktop environment are you running and are you using desktop effects? I found that desktop effects can be quite ressource intensive. If you use desktop effects, does it make a difference if turn them completely off?